The present invention relates to novel solvent systems, based on water-soluble amino derivatives and propylene glycol compounds, that are useful for removing photoresists.
Photoresists are used as masks in the production of, via etching or implantation processes, integrated component parts, circuit boards, and the like. After having served their purposes, the masks are generally removed, frequently by means of agents which, depending on their mode of action, are known as "strippers" or "removers".
Systems of this kind are described, for example, by W. S. de Forest in "Photoresist: Materials and Processes" pages 203 et seq., McGraw-Hill Book Co., New York, 1975. They contain, e.g., chlorinated hydrocarbons, such as methylenechloride; polar solvents, such as dimethylformamide, N-methyl-2-pyrrolidone and monoethanolamine; glycol ethers, such as ethylene glycol monoethyl ether, ethylene glycol monobutyl ether and the acetates thereof; strong bases, such as tetramethyl ammonium hydroxide; and strong acids, such as sulfuric acid/H.sub.2 O.sub.2 mixtures.
U.S. Pat. No. 3,673,099 describes a mixture of N-methyl-2-pyrrolidone and a strong base, such as tetramethyl ammonium hydroxide. It is known that mixtures of this type attack sensitive substrates, such as aluminum layers, when water is added. It is, however, desirable for a product to be suitable for removing photoresist coatings both from sensitive and less sensitive substrate layers, since quite frequently these two types of substrate layers are used simultaneously. Moreover, tetramethyl ammonium hydroxide easily decomposes when heated, and thus the stripping solution has a very short service life at elevated temperatures.
U.S. Pat. No. 3,796,602 describes a system comprising an organic solvent which is partially miscible with water. However, the compounds mentioned in this publication, such as ethylene glycol monobutyl ether and monoaminoethanol, present toxicological problems. Furthermore, these compounds evaporate easily due to their low boiling points and, hence, cannot be employed at elevated temperatures.
European Patent Application No. 0 075 329 describes a mixture of a derivative of 2-pyrrolidone and a diethylene glycol monoalkyl ether. Compounds of this kind are, however, hardly effective in their action. In the examples of the document, for instance, a stripper bath temperature of 75.degree. C. is required for removal of a photoresist subjected to a post-bake treatment at about 150.degree. C.
European Patent Application No. 0 145 973 describes a system of a piperazine derivative and a N-alkyl-2-pyrrolidone. The preferably employed N-aminoethyl piperazine is classified as being toxic, whereas n-hydroxyethyl piperazine is scarcely effective.